Method and apparatus of diametrically expanding metal shafts

ABSTRACT

Method and apparatus for diametrically expanding a desired part of a metal shaft which can be a rod or a pipe, wherein the apparatus includes a driving rotary section ( 4 ) and a driven rotary section ( 6 ) arranged at a predetermined distance (D), each of the rotary sections ( 4 ) and ( 6 ) including a holder for holding a work, a pressing device ( 8 ) for pressing the work held by the holders along the length of the apparatus, and a biasing device ( 7 ) for declining the axis of the work, so that the work held by the holders at the distance (D) is rotated around its axis, and one of the holders is forced by the pressing device toward the other to carry out the diametral expansion, and then the work is bent back and straightened up.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and apparatus fordiametrically expanding a desired portion, such as a middle portion, ofmetal shafts which can be solid like bars or tubular like pipes.

BACKGROUND ART

[0002] It is common practice to obtain a metal shaft having a locallyincreased diameter by machining a blank shaft of a relatively largediameter. However, this machining process disadvantageously takes time,and what is worse, tends to waste metal as cutting chips.

[0003] In general, the mechanical power transmission shafts require theprovision of components such as gears, cams, and sprockets whosediameter is larger than that of the shafts. In order to provide themetal shafts with these components, a mechanical method is noteconomical where the metal flesh of a shaft is machined to form gears asintegral parts. An alternative way is to produce those component partson a separate process, and join them to the shafts by welding orbolting. This method is not efficient. Therefore, a metallurgicalprocess was proposed for forcing a metal shaft to diametrically expandin a desired portion, and cutting gears or cams there. However, it hasbeen considered to be impracticable to put the proposed metallurgicalmethod in practice.

[0004] The inventor of the present application invented a method ofexpanding the diameter of a metal shaft in its middle portion throughrotation, bending and compression, which is disclosed in Japanese PatentNo. 1,993,956. This metallurgical method has overshadowed theconventional mechanical method, and made it possible to form gears orcams in the diametrically expanded portion of a metal shaft.

[0005] According to the previous invention referred to above, the metalshaft is subjected to rotation and bending under a sufficientcompression until a diametrically expanded portion is obtained, andafter the shaft is bent back, the rotation and bending are stopped. Ifthe compressive force is too large, the shaft must be held firmly towithstand it. In contrast, if it is too low, an increased number ofrotations is required until a desired shape is obtained, thereby takinga long time before the desired portion of the shaft is diametricallyexpanded. A further disadvantage is the lack of precision involved in apair of rotary holders provided in the apparatus, one having a biasingmeans for bending the work, and the other having a pressing means forcausing one holder to approach the other.

[0006] Accordingly, one object of the present invention is to provide amethod and apparatus capable of performing a local diametral expansionof a metal shaft efficiently and accurately.

[0007] Another object of the present invention is to provide a methodand apparatus capable of careful inspection of deformation likely tooccur in a metal shaft in view of the insufficient analysis on themechanism of the diametral expansion of a metal shaft.

[0008] A further object of the present invention is to provide a methodand apparatus capable of diametrically expanding a portion of a metalshaft to a collar-like shape of any size.

[0009] A still further object of the present invention is to provide amethod and apparatus capable of diametrically expanding a metal shaftwith no detrimental torsion in the metal shaft, which would otherwisedecrease the tensile strength of the metal shaft after the diametralexpansion is finished. The torsion results from the fact that one of therotary holders is subjected to a torque which is transmitted to theother holder through the solid work.

[0010] Another object of the present invention is to provide a methodand apparatus capable of diametrically expanding a metal shaft with useof a conventional lathe.

SUMMARY OF THE INVENTION

[0011] The present invention provides a method for diametricallyexpanding a predetermined part of a metal shaft, including the steps ofholding the shaft between a pair of holders spaced at a distance (D);rotating the work around its axis, moving one of the holders toward theother holder so as to compress the work; biasing one of the holders in adirection which crosses the axis of the other holder, so as to bend thework and build up bulged portions accruing inside the bent portionaround the periphery of the work within the distance (D) until a desiredexpansion is achieved; and straightening up the work, wherein thecompression is constantly applied to both the inner and outer sides ofthe work to be bent, and the rotation is initiated at the latestimmediately after the bending is started, and the straightening-up isperformed under the continued compression and rotation.

[0012] In this case, the compression is relatively low at the initialstage of the diametral expansion, and increases in accordance with theadvance-of the expansion.

[0013] The present invention also provides an apparatus for carrying outthe above-mentioned method, including a driving rotary section and adriven rotary section arranged at a predetermined distance, each of therotary sections comprising holders for securing a work therebetween; adriver for operating the driving rotary section; a pressing device foraxially compressing the work held by the holders; and a biasing devicefor declining the axis of the work; wherein the pressing device appliesthe compression to one of the rotary sections, and the biasing devicedeclining the other rotary section.

[0014] According to another aspect of the invention, the apparatusincludes a driving rotary section and a driven rotary section arrangedat a predetermined distance, each of the rotary sections comprisingholders for securing a work therebetween; a driver for operating thedriving rotary section; a pressing device for axially compressing thework held by the holders; and a biasing device for declining the rotarysection so as to cause the work to decline with respect to its axis;wherein either the driving rotary section or the driven rotary sectionis arranged rotatably around a pivot provided in a directionperpendicular to the axis of the work, and the rotatably arranged rotarysection is supported by the pivot so as to enable the simultaneousinspection of the inner and outer sides of the bent portion of the work.

[0015] As a further preferred embodiment the apparatus can be providedwith a slidable frame on the base plate, and a rotary frameworkrotatably connected to the slidable frame through a bearing, and whereinthe driving rotary section is secured to the base plate and the drivenrotary section is secured to the rotary framework.

[0016] As another preferred embodiment, especially suitable forprocessing a work having a relatively large diameter, the apparatusincludes a driving rotary section and a driven rotary section arrangedat a predetermined distance, each of the rotary sections comprisingholders for securing a work therebetween; a driver for operating thedriving rotary section; a pressing device for axially compressing thework held by the holders; and a biasing device for declining the rotarysection so as to cause the work to decline with respect to its axis;wherein the pressing device applies the compression to one of the rotarysections, and the biasing device declining the other rotary section.

[0017] In this case, the apparatus can be provided with a displacingdevice for shifting the center of rotation between the holders inaccordance with a sliding distance covered by the pressing device.

[0018] As a further preferred embodiment the apparatus includes a pairof rotary sections; a holder provided in each of the rotary sections forholding a work; a sliding device for causing at least one of the rotarysections to move toward and away from the other rotary section; abiasing device for declining at least one of the rotary sections withrespect to the axis of the other rotary section; a driver for rotatingthe work held by the holders around its axis; and a transmission fortransmitting the torque of one rotary section to another so as to effectthe synchronous rotation of the two rotary sections.

[0019] More specifically, the transmission includes a rotating divisionin which rotatable brackets are provided, having a pair of splinesinterposed between them, the splines comprising gears engaged withfollower gear provided in the rotating division, thereby transmitting atorque of one of the rotating division to the other.

[0020] As a more practical embodiment the apparatus includes a drivingrotary section provided with a first work holder and being capable ofrotating the work held by the holder; a driven rotary section providedwith a second work holder on an opposite side to the holder of thedriving rotary section and being capable of moving toward and away fromthe driving rotary section; a biasing device for declining the secondholder with respect to the axis of the first holder; and a pressingdevice for pressing the driven rotary section toward the driving rotarysection; wherein the driving rotary section is driven by an arrangementin which the first work holder is connected to a chuck of a lathe so asto utilize the torque of the lathe.

[0021] In this case the pressing device is preferably placed between abase plate and a slidable frame, and wherein the base plate is providedwith a tapered shaft, the tapered shaft and the first work holder beingconnected to the lathe, thereby compensating a repulsive force involvedin operating the pressing device within the base plate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIGS. 1a to 1 d are schematic views explaining the process ofperforming a method according to the invention;

[0023]FIG. 2 is a plan view of an apparatus according to the invention;

[0024]FIG. 3 is a side view of the apparatus shown in FIG. 2;

[0025]FIG. 4 is a cross-sectional side view of a rotary holderincorporated in the apparatus shown in FIG. 2;

[0026]FIG. 5 is a plan view of the rotary holder shown in FIG. 4

[0027]FIG. 6 is a plan view of an apparatus according to anotherembodiment of the invention;

[0028]FIG. 7 is a side view of the apparatus shown in FIG. 6;

[0029]FIG. 8 is a cross-sectional side view of the apparatus shown inFIG. 6;

[0030]FIG. 9 is a cross-sectional side view of a driving rotary sectionincorporated in the apparatus shown in FIG. 6;

[0031]FIG. 10 is a cross-sectional side view of a driven rotary sectionincorporated in the apparatus shown in FIG. 6;

[0032]FIG. 11 is a plan view of a feeder incorporated in the apparatusshown in FIG. 6;

[0033]FIG. 12 is a perspective view of chucks incorporated in theapparatus shown in FIG. 6;

[0034]FIG. 13 is a side view of a modified version of chucksincorporated in the apparatus shown in FIG. 6;

[0035]FIG. 14 is a schematic view of the apparatus shown in FIG. 6 whenit is in the process of performing the diametral expansion;

[0036]FIG. 15 is a plan view of the apparatus shown in FIG. 6 when theprocess is finished;

[0037]FIG. 16 is a plan view of an apparatus according to a furtherembodiment of the invention;

[0038]FIG. 17 is a cross-sectional side view of the apparatus shown inFIG. 16;

[0039]FIG. 18 is a plan view of a slidable framework and a rotaryframework (shown in imaginary lines) incorporated in the apparatus shownin FIG. 16;

[0040]FIG. 19 is a cross-sectional side view of the arrangement shown inFIG. 18;

[0041]FIG. 20 is a schematic view explaining the process of performingthe diametral expansion according to the embodiment shown in FIG. 16;

[0042]FIG. 21 is a plan view of a still further embodiment of theinvention;

[0043]FIG. 22 is a cross-sectional side view of the apparatus shown inFIG. 21;

[0044]FIG. 23 is a perspective view of another embodiment of theinvention;

[0045]FIG. 24 is a plan view of the apparatus shown in FIG. 23;

[0046]FIG. 25 is a cross-sectional side view of the apparatus shown inFIG. 23;

[0047]FIG. 26 is a plan view of a slidable framework and a slidingdevice incorporated in the apparatus shown in FIG. 23;

[0048]FIG. 27 is a plan view of a rotary frame and a biasing deviceincorporated in the apparatus shown in FIG. 23;

[0049]FIG. 28 is a cross-sectional view taken along the line A-A in FIG.24;

[0050]FIG. 29 is a cross-sectional view of a transmission incorporatedin the apparatus shown in FIG. 23;

[0051]FIG. 30 is a plan view of an apparatus according to a furtherembodiment of the invention;

[0052]FIG. 31 is a schematic view of the apparatus shown in FIG. 30 whenit is in the process of performing the diametral expansion;

[0053]FIG. 32 is a perspective view of an apparatus according to a stillfurther embodiment of the invention;

[0054]FIG. 33 is a plan view of the apparatus shown in FIG. 32;

[0055]FIG. 34 is a cross-sectional side view of the apparatus shown inFIG. 32;

[0056]FIG. 35 is a cross-sectional side view explaining the process ofperforming the diametral expansion according to the embodiment shown inFIG. 32;

[0057]FIG. 36 is a side view of a lathe connected to the apparatus shownin FIG. 32;

[0058]FIG. 37 is a cross-sectional side view of an apparatus accordingto a still further embodiment of the invention;

[0059]FIG. 38 is a plan view of the apparatus shown in FIG. 37;

[0060]FIG. 39 is a cross-sectional side view explaining the process ofperforming the diametral expansion;

[0061]FIG. 40 is a schematic cross-sectional view explaining the firststep of performing the diametral expansion where a work is mounted onthe apparatus;

[0062]FIG. 41 is a schematic cross-sectional view explaining the secondstep where the work is subjected to rotation, compression and bending;

[0063]FIG. 42 is a schematic cross-sectional view explaining the thirdstep where the work is subjected to the continued rotation, compressionand bending;

[0064]FIG. 43 is a schematic cross-sectional view explaining the fourthstep where the work is subjected to straightening up under the continuedrotation and compression); and

[0065]FIG. 44 is a cross-sectional view of a finished diametricallyexpanded portion of the work.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Referring to FIGS. 1a, 1 b, 1 c and 1 d, respectively, theprinciple underlying the present invention will be described:

[0067] A pair of holders are co-axially arranged or aligned to hold awork (W) between them, wherein the work (W) can be solid or tubular. Theholders are spaced by a distance (D) (FIG. 1a). Then, compression isaxially applied until the work (W) is inwardly bent between the holders,and rotation is imparted to it as shown in FIG. 1b. The bendingdiametrically expands a portion in the work. The applied compressionnegates a possible pull which would otherwise act on the work, andtherefore is stepped up. The rotation is effective to equal thediametral expansion around the periphery of the work (W). To this end,it is preferable that the work (W) is rotated while being subjected tothe compression. The rotation can be started at any time.

[0068] The work (W) kept in the above-mentioned conditions is rotatedseveral times. The sides of the diametrically expanded portion extendsto each holding part, and are subjected to the compression. In this waythe compression is stepped up. This means that the initial compressiveforce can be low, thereby reducing the holding force of each holder uponthe work (W). As the compression is continued, the compressive forceincreases to shorten the operation hour (FIG. 1c). After the desireddiametral expansion is finished, the work (W) is bent back until itbecomes straight while the compression and rotation are repeated asshown in FIG. 1d. After the work (W) is straightened up, the rotationand compression are stopped, wherein either stoppage can be earlier thanthe other.

[0069] Referring to FIGS. 2 to 5, a first preferred embodiment of thepresent invention will be more particularly described:

[0070] The illustrated apparatus is a collar forming apparatus(hereinafter ‘apparatus’) 1 which is provided with a stand 2 on a floor,a rotary framework 3 axially slidable on the stand 2, a driving rotaryholder 4 mounted on the rotary framework 3 and driven by a motor 5, anda driven rotary holder 6 located on the opposite side to the drivingrotary holder 4, a biasing device 7 for declining the driven rotaryholder 6 with respect to the axis of the driving rotary holder 4, and apressing device 8 for pressurizing the driving rotary holder 4 towardthe driven rotary holder 6; in other words, for compressing the drivingrotary holder toward the driven rotary holder 6.

[0071] The stand 2 is composed of pillars 10 which are mounted on baseplates 9, and parallel rails 11 spacedly arranged between which thepressing device 8 is fixed to a first support 12 at a front section ofthe apparatus 1. The driven rotary holder 6 is fixed to a second support13 in the middle of the apparatus 1. The second support 13 is providedwith a bore 13 a in which a pivot 14 rests so as to allow the holder 6to rotate.

[0072] The rotary framework 3 mounted on the stand 2 includes sideframes 15 axially arranged, transverse frames 16 fixed on the top of theside frames 15, and a stand 17 on which a motor is mounted. The rotaryframework 3 is crosswise limited by the side frames 15, and verticallylimited by the transverse frames 16. In this way the axial movement ofthe rotary framework 3 is effected along the rails 11. Preferably, alower framework 18 is provided in a lower part of the framework 16.

[0073] The driving rotary holder 4 is provided on the rotary framework3. The holder 4 includes a supporting sleeve 20 rotatably carried withina sleeve 19 secured to the rear framework 16. The supporting sleeve 20is provided with a chamber 20 a whose end is outwardly tapered at anangle is α° toward the other holder 6, and also provided with a threadedportion 20 b on and around the tapered end. The chamber 20 houses chucks21 each of which has a tapered outside wall corresponding to the taperedinside wall of the chamber 20 a. The chuck 21 is obtained by splittingthe body into a plurality of portions and forcefully inserted in thechamber 20 a. The end portion of the holder 20 is covered with afastening nut 22 with its inner space 21 a being open. The work (W) isforced into the inner space 21 a, and becomes held therein.

[0074] The rotary holder 4 is associated with a driving means 5, whichis an electric motor 23 in the illustrated embodiment, to receive adriving force therefrom. The motor 23 has an output shaft provided witha driving gear 24 engaged with a driven gear 25 located in the front endof the holder 20.

[0075] Being arranged opposite the driving rotary holder 4, the drivenrotary holder 6 has the same structure as the holder 4. The holder 6 isfixed to a rotary plate 26 connected to the pivot 14 which is carried inthe bore 13 a of the second support 13. In this way the holder 6 isrotated in such a manner that it become biased with respect to its axis.The holders 4 and 6 are aligned, and ratable around the pivot 14.

[0076] The biasing device 7 is provided to rotate the driven rotaryholder 6. It includes a nut 28 rotatably connected to a bracket 27 of arear end of the rotary plat 26, a motor 30 secured to a rotary plate 29provided on the rails 11, the output shaft of the motor 30 having athread portion 21 engaged with the nut 28. The rotation of the motor 30in either direction causes the thread portion 21 to rotate around therotary plate 26, but the nut 28 does not rotate because of its fixationto the bracket 27. In this way the driven rotary holder 6 is rotated ina horizontal plane. The biasing device 7 is not limited to thisembodiment but can be a version in which the rotary holder 6 is rotatedaround the pivot 14 with the addition of a link-system pressing deviceor a fluid-system pressing device which causes the work (W) to becomebiased by applying a force to it in a directon which crosses the axis ofthe work (W).

[0077] The pressing device 8 is provided in the rear lower part of thedriving rotary holder 4. This device 8 compresses the driving rotaryholder 4 toward the driven rotary holder 6. It is constructed with adouble-acting hydraulic cylinder 32 secured to the stand 2 at one endand to the slidable framework 3 at the other end. Instead of thehydraulic cylinder 32, a hydraulic jack or a fluid cylinder can beemployed.

[0078] No controller is illustrated in the drawings for the motors 23and 30, and the hydraulic cylinder 32 but it can be designed tooptionally set the rotations per minute of each motor 23 and 30 and apressure provided by the cylinder 32. The angle of the biasing device 7can be adjusted as desired.

[0079] In making a desired local diametral expansion, the rotary holders4 and 6 are aligned, and the chucks 21 of both holders are spaced at apredetermined distance (D) between which a work (W) is placed, and heldby the nut 22.

[0080] The hydraulic cylinder 32 is operated so that the work (W) isbent until it is compressed. Then the motor 30 is driven to further bendthe work (W) at 3 to 7°. The time for driving the motor 30 is optional.

[0081] The rotation continues several times, thereby causing the localdiametral expansion to grow and at the same time, subjecting itssurrounding to the compressive pressure. Therefore, no slip occursbetween the work (W) and the chucks 21 in spite of an increase incompression. Owing to the increased compressive pressure, the localdiametral expansion can be finished in a short time.

[0082] When the local diametral expansion is finished, the work (W) isbent back to straighten up. Then the motor 23 and the hydraulic cylinder32 are deenerzied.

[0083] The work (W) is withdrawn out of the holders simply by looseningthe nut 22.

[0084] As evident from the foregoing description, the apparatus of theinvention does not require a large force for holding the work (W),thereby allowing the employment of a simplified mechanism. In addition,owning to the separate provision of the presser and the biasing device,a high degree of precision is achieved in the local diametral expansion.

[0085] FIGS. 6 to 15 show another embodiment of the present invention.The illustrated apparatus 101 is provided with a stand 102 on a floor, adriver section 103 mounted on the stand 102 driven by a driving unit104, a driven rotary section 105 located opposite supported by aslidable framework 106 and a rotary framework 107, a biasing device 108provided between the framework 106 and the rotary framework 107 to causethe work (W) to become biased, and a pressing device 109 provided in therear end of the driven rotary section 105.

[0086] The stand 102 includes pillars 111 erected on plates 110, andframes 112 arranged in parallel along the length of the apparatus on thetop of the pillars 1 11, a driving means mount 113 in and between frontends of the frames 112, a driving rotary section mount 114 in its rearend, and a nut 115 for slidable use in the rear end of the mount 114.

[0087] The driver section 103 includes an outer sleeve 116 in which aninner sleeve 117 is rotatably carried. The inner sleeve 117 has femalethreads on its inside wall which is tapered at α° at the end. The innersleeve 117 houses a pair of chucks 118 for holding the work (W). Thechuck 118 is made by splitting one body into a plurality of chuckpieces, each of which is tapered at α°. A hollow core 119 is inserted inthe inner sleeve 117 such that it can push the inner sleeve by a hollowbolt 120. By fastening the bolt 120, the chucks 118 are moved by thecore 119, so that the tapered top ends of the chucks 118 are restrictedto press the work (W).

[0088] The driving unit 104 includes a driven gear 121 in the front endof the inner sleeve 117, and the driving means mount 113 includes amotor 122 whose output shaft having a thread 123 engaged with the drivengear 121.

[0089] Opposite the driver section is provided a driven rotary section105 secured to the rotary framework 107, which is provided on theframework 106 arranged between the frames 112.

[0090] The framework 106 is provided with a feeder 124 designed to causethe driven rotary section 105 to approach or separate from the driversection 103. The feeder 124 is provided with a pair of bearings 125 and126 on opposite ends between which a feed screw 127 is carried inengagement with a nut 115 provided on the stand 102. The feeder screw127 is rotatable in either direction, thereby causing the framework 106to move along the length of the apparatus. The rear end of the feederscrew 127 is connected to an output shaft of a motor 128 provided on theframework 106. The energization of the motor 128 drives the feeder screw127.

[0091] The biasing device 108, designed to cause the work (W) to becomebiased with respect to its axis, rotates the rotary framework 107, whichis integral with the driven rotary section 105, in a horizontal plane onthe top surface of the frames 112. The biasing device 108 includes apivot 107 a in a bore 106 a produced in the framework 106 such that therotary framework is rotatable around the pivot 107 a. A nut 129 isfitted in an opening 106 b in the rear end of the framework 106, and amotor 131 is provided on a bracket 130 secured to the rotary framework107. The output shaft of the motor 131 is provided with a thread portion132 which is engaged with he nut 129. The rotation of the motor 131 ineither direction causes the thread portion 132 to rotate in a clockwiseor anti-clockwise direction. Since the nut 129 is rotatably connected tothe framework 106, the nut 129 does not move, and the thread portion 132rotates the rotary framework 107. In this way the driven rotary section105 rotates in a horizontal plane around the pivot 107 a. The biasingdevice 108 is not limited to this embodiment, but can be a version inwhich the driven rotary section 105 is rotatable around the pivot 107 aunder a linkage pressing system or a fluid cylinder, thereby applyingforce to the work (W) at right angle to its axis, thereby causing thework to become biased.

[0092] The driven rotary section 105, secured to the upper part of therotary frame 107, includes an outer sleeve 133 in which an inner sleeve134 having an inside space 134 a is rotatably housed. The inner sleeve134 has an inside wall tapered at β° at its front end. The inner sleeve134 houses chucks 135 for holding the work (W). The chucks 135 areproduced by splitting a hollow cylinder into a plurality of chuck pieceswhose outsides are tapered at β°. The chuck pieces are compressed by thepressing device 109, thereby holding the work (W) in a restricted space134 a.

[0093] The number of split chuck pieces can be two as shown in FIG. 12or three as shown in FIG. 13.

[0094] The pressing device 109, provided in the rear end of the drivenrotary section 105 to push the driven rotary section 105 toward thedriver rotary section 103 by means of a hydraulic cylinder 136 providedon the rotary framework 107. The hydraulic cylinder 136, designed topush the holder 134 toward the driver rotary section 103, has a pistonrod 136 a engaged with an inner bearing 137 around which an outerbearing 138 is provided in engagement with the inner sleeve 134, so asto avoid transmitting the rotation of the inner sleeve 134 to the pistonrod 136 a. As alternatives of the pressing device 109, a hydraulic jackor a fluid cylinder can be employed.

[0095] No controller for the motors 122, 128 and the hydraulic cylinder136 is illustrated in the drawings, but it can be designed to optionallyset the rotations per minute of each motor and a pressure provided bythe cylinder. The angle of the biasing device can be adjusted asdesired.

[0096] Instead of constructing the biasing device such that it rotatesthe work in a horizontal plane, the rotary pivot is constructed suchthat it vertically rotates around the horizontal axis perpendicular tothe work (W), thereby enabling an operator to inspect the state of thediametral expansion in progress from the side of the apparatus.

[0097] In making a desired local diametral expansion by using theapparatus 101, the driver rotary section 103 and the driven rotarysection 105 are arranged such that the inner sleeves 117 and 134 arealigned. The work (W) is inserted between the chucks 118 opened byloosening the hollow bolt 120 to expand the chucks 118. Then the targetportion for the local diametral expansion is specified by placing thatportion flush with the end face of the chucks, followed by fastening thebolt 120 to hold the work (W) in the chucks 118. Then, the feeder 124 isoperated to move the driven rotary section 105 toward the driver rotarysection 103, and allows the work (W) to become held by its chucks 135,wherein the driver rotary section 103 and the driven rotary section 195are appropriately spaced. Then the motor 112 is operated to rotate theinner sleeve 117, thereby causing the work (W) held by the chucks 118 torotate. The driven chucks 135 are also rotated. The work (W) is axiallypressured by the pressing device 109, and the driven rotary section 105becomes biased by the biasing device 108 as shown in FIG. 14. In thisway, when both the pressing device 109 and the biasing device 108 areput into operation, the work (W) held by the chucks 118 and 135 arerotated and compressed in its bent position. The rotating speed can be afew tens of times per minute, and the bending angle θ can be 3° to 7°.The amplitude of pressure depends upon the diameter of the work. Ingeneral, a local diametral expansion is possible with a pressure equalto about 20% to 30% of the stress at which a single metal shaft reachesa yield point as taught in Technical Reports entitled “Study onDiametral Expansion of a Bar” (Vol. 34 by Nih'hama Technical Academy).

[0098] In this way the work (W) is subjected to rotation, bending, andpressuring between the chucks 118 and 135, thereby effecting a localdiametral expansion of this part of the work. As the local diametralexpansion advances, the distance between the chucks 118 and 135 becomesshort while the work is constantly subjected to pressuring. If thepressure is reduced at this moment, the outside and the inside aroundthe bent portion are alternately subjected to bending and straightening,thereby resulting in the breakdown of the work (W). After the desiredlocal diametral expansion is finished, the biasing device 108 isreturned to its original position (i.e. where the rotary sections 103and 105 are aligned) while the rotation and pressuring are repeated. Asa result, the work (W) having a diametrically expanded portion isobtained as shown in FIG. 15. Finally, the rotation and compression arestopped, and the work (W) is taken out of the chucks 135.

[0099] FIGS. 16 to 22 show a further preferred embodiment of the presentinvention. The illustrated apparatus 201 is provided with a stand 202 ona floor on which pillars 203 are erected to support a rectangularframework 204. A driving rotary section 205 is mounted on the front partof the framework 204 (the left-hand part in FIG. 16), and a mount 207for a slidable pressing device 206 is fixed to the rear part of theframework 204. The framework 204 includes grooves 208 a on opposite side208.

[0100] The driven rotary section 205 includes a cylindrical sleeve 211rotatably supported on a sleeve body 210 secured to a member 209 of theframework 204, the sleeve 211 being provided with a follower gear 212.The sleeve 211 houses chucks 213 designed to hold a work (W). The sleeve211 and the chucks 213 are provided with tapered portions for the samereason referred to above.

[0101] A motor 214 is provided in a lower part of the sleeve 211 as apower source for rotating the work (W), having an output shaft beingprovided with a gear 215 engaged with the follower gear 212.

[0102] A slidable framework 216 moves toward and away from the drivingrotary section 205, as the case may be. The framework 216 issubstantially rectangular, and its side frames 217 are provided withprojections to be fitted in the groove 208 a of the frame 204. Betweenthe side frames 217 is provided an intermediate member 218 with aninside space 218 a. The frame 204 is slid by a double-acting hydrauliccylinder 219 provided between the mount 207 and the intermediate member218. The hydraulic cylinder 219 is supported by a holder 220 secured tothe slidable framework 216. The contraction and expansion of thehydraulic cylinder 219 cause the framework 216 to move to and fro alongthe length of the apparatus 201.

[0103] On top of the framework 216 is a rotary framework 221, whichsecures a pair of rails 224 provided with a groove 224. The rails 224are provided with a hydraulic cylinder 227 at their rear ends through amount 228, which functions as a pressing device 226 for a driven rotarysection 225, hereinafter referred to. The rotary framework 221 isrotatably connected to the slidable framework 216.

[0104] The driven rotary section 225 is located opposite the drivingrotary section 205 on the framework 221. The driven rotary section 225has the same construction as the driving rotary section 205, whereinlike reference numerals denote like components. The sleeve 210 of thedriven rotary section 225 is slidable along the rails 224 on theframework 221 through engagement of a projection of a member 229 in thegrooves 224 a. A hydraulic cylinder 227 as the pressing device 226 isprovided. The contraction and expansion of the cylinder 227 causes thedriven rotary section 225 to move to and fro along the length of theapparatus.

[0105] In this embodiment the hydraulic cylinder is employed for apressing device but instead of it, a screw type feed system can be used.

[0106] The reference numeral 230 denotes a biasing device 230 whichincludes a member 231 rotatably fitted in an inside space 220 a of theholder 220 in the framework 216, ad a nut 22 rotatable in an insidespace 224 b produced in the rails 224 with the additional provision of amotor 233 whose output shaft is provided with a male thread portion 234engaged with the nut 232. The rotation of the motor 233 in eitherdirection causes the male thread portion 234 to rotate, followed by themovement of the nut 232. In this way the rotary framework 221 is rotatedaround a pivot 223, thereby causing the driven rotary section 225 on therotary framework 221 to rotate.

[0107] No controller is illustrated in the drawings for the motors 214and 233 and the hydraulic cylinder 219, 227. However, these motors 214,233 are designed to control their clockwise or anti-clockwise rotationson their own, and the hydraulic cylinders 219, 227 to control the amountof their movement on their own.

[0108] In this embodiment the work (W) is rotated through the drivingrotary section 205 driven by the motor 214. The driven rotary section225 is caused to move toward and away from the driving rotary sectionwhile being biased by the biasing device 230 with respect to the axis ofthe driving rotary section 205. When the pivot 223 approaches thedriving rotary section 205, the driven rotary section 225 is caused toapproach the pivot 223 by the second pressing device 226. This meansthat the axis of the pivot 223 can be appropriately located between thetwo chucks 213 of the holders 205 and 225 by adjusting the slidingdistance of the pressing devices 206 and 226.

[0109] In this embodiment the operation of the apparatus 201 isinitiated by aligning the two rotary sections 205 and 225. Then, thework (W) is inserted between the chucks 213 in the holders 205 and 225.The motor 214 is energized to rotate the work (W). The pressing devices206 and 226 are operated to compress the work (W), and biasing device230 is operated to bend it, wherein the compressive force is such thatno pull occurs around the bent portion or at least a load to the work(W). If the compressive force is weak, the work (W) is subjected torepeated compression and extension, and is finally liable to fracture. Adesired local diametral expansion of the work (W) is finished, therotary sections 205 and 225 are aligned by the biasing device 230 whilethe compression and rotation are continued so as to straighten up thework. Finally, the work (W) is taken out of the holders 213 bycontracting either of the pressing device 206 or 226.

[0110] As shown in FIG. 20, the driven rotary section 225 approaches thedriving rotary section 205 by the pressing device 206 which causes theframework 216 to approach the driving rotary section 205. Furthermore,the driven rotary section 225 approaches the pivot 223 by the framework221 by the pressing device 226. This means that the approach of thedriven rotary section 225 to the pivot 223 causes the driven rotarysection 225 to approach the pivot 223. In this way the axis of the pivot223 as the point of bend is located in the middle between the chucks213. This ensures that the local diametral expansion of the work occursin the middle between the chucks 213. This prevents the loss of theexpanding force.

[0111]FIGS. 21 and 22 show a further preferred embodiment, where,instead of the driving rotary section 205 secured to the framework 204,the intermediate member 218 for the pivot 223 is secured to theframework 204, and the framework 221 is rotatably connected to theintermediate member 218. In addition, the driven rotary section 225 isarranged to move toward and away from the pivot 223 on the rotaryframework 221, and the slidable framework 216 is constructed to movetoward and away from the pivot 223 along the sides 208 of the framework204, and the driving rotary section is secured to the slidable framework216. In this embodiment the axis of the pivot 223 is adequately locatedbetween the chucks 213 by adjusting a distance over which the pressingdevices 206 and 226 have slid. FIGS. 21 and 22 like reference numeralsdesignate like elements and components to those of the above-mentionedembodiments, and therefore, a description will be omitted forsimplicity.

[0112] When the sliding distances of the pressing devices 206 and 226are equalized, the axis of the pivot as the point of bend isadvantageously located in the middle between the chucks 213 foreffecting a diametral expansion of a metal shaft.

[0113] FIGS. 23 to 29 show a still further preferred embodiment. Theillustrated apparatus 301 is provided with stands 302 on which pillars303 are erected to support a rectangular framework 304. A groove 305 ais provided between the opposite sides 305 of the framework 304 alongthe length of the apparatus 301. The framework 304 is provided with amotor mount 306 and a front bracket 307 in its front section, and a rearbracket 308 in its rear section. The reference numerals 309 designatereinforcements.

[0114] Between the sides 305 are arranged a slidable framework 310 and asliding device 311 for causing the framework 310 to slide along thelength of the apparatus 301. The slidable framework 310 includes sideframes 312 having a projection 312 a fitted in the groove 305 a, and anintermediate member 313 having an opening 313 a vertically formed and asupport 314 for the sliding device 311.

[0115] The sliding device 311 is provided in the form of a double-actinghydraulic cylinder 315 on the side of the intermediate member 313. Thehydraulic cylinder 315 is supported by the support 314, and is securedto the rear bracket 308. In this way the extension and contraction ofthe hydraulic cylinder 315 cause the slidable framework 310 to slidealong the length of the apparatus 301. The hydraulic cylinder 315 can besubstituted by other suitable means such as a screw-base system feeder.

[0116] A rotary framework 316 is carried on the slidable framework 310.The rotary framework 316 includes a plate member 317, and a rotary pivot318 rotatably fitted in the inside space 313 a. A biasing device 319 isprovided in a rear section of the rotary framework 316. The biasingdevice 319 includes a plate 320 in which inside spaces 320 a areproduced to accept shafts 321 a, with a feed nut 321 having a femalethread 321 b inside.

[0117] The slidable framework 310 includes an inside space 312 b in itssides 312 in which a mount 322 is provided on which a motor 323 ismounted. The motor 323 has an output shaft is provided with a malethread 324 engaged with the feed nut 321. In this way the rotation ofthe motor 323 in either direction causes the feeder nut 321 to movetoward and away from the motor 323 whereby the rotary framework 316 isrotated around the pivot 318.

[0118] Rotors 325 and 326 are aligned on the front bracket 307 and theplate member 317. Each of the rotors 325 and 326 includes a rotableinner sleeve 329 in an outer sleeve 328. The inner sleeve 329 isprovided with the tapered portion on the inside wall with which chucks331 are engaged. The chucks 331 are formed by splitting a sleeve memberhaving a tapered portion matching with that of the inner sleeve 329 intoseveral chuck pieces.

[0119] A driving device 332 is provided to drive a holder 330 of therotor 325, the driving device including a follower gear 333 in the innersleeve 329. The inner sleeve 329 of the other rotor 326 has a similarfollower gear 333. There is provided a motor 334 whose output shaft isprovided with a driving gear 335 engageable with the follower gear 333so as to transmit a torque to the rotor 325. The torque transmitted tothe follower gear 333 is transmitted to the rotor 326 through atransmission 336, which includes metals 337 secured to the outer sleeves328, and brackets 338 rotatably fitted in an inside space 307 a producedin a front framework 307 of a framework 304 and an inside space 317 a inthe plate member 317 of the rotary framework 316. The bracket 338 isprovided with bearings 338 b which carry a pair of splines 339 havingteeth 340 engaged with the follower gears 333. The transmission 336transmits a torque of the rotor 326 to the other rotor 325 as the formermoves in either direction or is biased, through engagement of thefollower gears 333 and gears 340.

[0120] No controller for the hydraulic cylinder 315, the motors 323 ofthe biasing device 319, and the motor 332 for driving the apparatus isillustrated in the drawings but any other controlling means can beemployed singly or in combination if it can start and stop them asdesired.

[0121] In this embodiment a single driving force is transmitted to therotors 325 and 326 but a modified version as shown in FIG. 30 is alsopossible in which a motor 341 is provided on the rotary framework 316,with its output shaft having a driving gear 342. The driving gear 342 isengaged with the follower gear 333, and the motors 334 and 341 arecontrolled by a controller (not shown), thereby effecting thesynchronous rotation of the rotors 325 and 326.

[0122] Referring to FIG. 31, the procedure for performing the diametralexpansion of a shaft by using this embodiment will be described:

[0123] The chucks 331 are aligned and a work (W) is inserted betweenthem. The chucks 331 firmly holds the work (W) under the taperedstructure of the inner sleeve 329. The distance between the chucks 331is maintained at D. Then the motor 334 is energized to cause the work(W) to rotate around its axis, and the rotor 326 is caused to approachthe rotor 325 until a compressive force P is applied to the work (W). Atthis stage, the bracket 338 of the transmission 336 is caused toapproach the other bracket in accordance with the sliding of theslidable framework 310, thereby shortening the distance of the twobrackets. The spline 339 is also shortened, wherein the rotorssynchronously rotate because of engagement of the gears 340 with thefollower gears 333, as shown in FIG. 31(a).

[0124] Subsequently, the biasing device 319; that is, the motor 323 isenergized to rotate the male thread 324 so as to disengage the feedernut 321 from it, thereby allowing the rotary framework to rotate aroundthe pivot 318. In this way the rotor 326 secured to the rotary framework316 is rotated in a biased position with respect to the axis of therotor 325. The brackets 338 of the rotors 325 and 326 are rotated suchthat the axes of the bearings 338 a are aligned, and because of theconstant engagement of the follower gear 333 with the gear 340, thesynchronous rotation of the rotors 325 and 326 is maintained as shown inFIG. 31(b).

[0125] While the work (W) is rotated, a bulged portion in the workgradually grows around the periphery of it and finally becomesdiametrically expanded as desired. The distance between the chucks 331is shortened, and the compressive force diminishes. As it becomessmaller than a pull occurring outside the bent portion of the work (W),it is subjected to straightening, and is liable to breakage. To avoidthe breakage, the work is kept under the compression (FIG. 31(c)).

[0126] Upon the achievement of the desired diametral expansion the motor323 is reversibly rotated, and the chucks 331 are aligned so as tostraighten the work (W) under the continued compressive force P. In thiscondition the work is rotated several times, thus obtaining astraightened work. Then the rotation and application of the compressiveforce are stopped, and the work is taken out by separating the rotor 325from the rotor 326 or vice versa by the hydraulic cylinder 315. The work(W) is readily released from the chucks 331, as shown in FIG. 31(d)).

[0127] FIGS. 32 to 36 show another preferred embodiment in which a latheis employed. A diametrically expanding apparatus 401 is connected to alathe (M) (not shown in FIGS. 32 to 35) through a structure in which abase plate 403 is provided for supporting a tapered shaft 402 designedto receive a tail stock of the lathe (M). The base plate 403 consistsmainly of parallel side frames 404 along the length of the apparatus,and a front transverse frame 405 and a rear transverse frame 406. Anouter sleeve 408 is secured to the front transverse frame 405 forsupporting a driving rotary section 407, and the tapered shaft 402 issecured to the rear transverse frame 406 in alignment with the taperedshaft 402. A pressing device 409 is supported on a mount 410 secured tothe rear transverse frame 406.

[0128] The driving rotary section 407 consists of an arrangement inwhich an inner sleeve 411 rotatably carried in the outer sleeve 408. Theinner sleeve 411 houses chuck sleeves 412 for holding a work (W) in aspace whose side wall is tapered at α°. The inner sleeve 114 is providedwith a male thread engageable with a female thread of a ring 413,wherein the engagement of the threads prevents the inner sleeve 411 fromdeviation along the length of the apparatus. The front part of theapparatus mentioned above is connected to a chuck (T) of the lathe (M)so as to transmit a torque of the lathe (M) to the driving rotarysection 407. In order to secure the transmission of the torque, thefront end of the inner sleeve 411 is made multi-angular in accordancewith the number of pawls of the lathe chuck; in the illustrated example,triangular in accordance with the three pawls. A cornered shape iseffective to transmit a torque with the minimum loss.

[0129] The chuck sleeves 412 includes an inside space 412 a in which thework (W) is placed, and it is split into several chuck pieces so as tohold the work (W) among them. After the work (W) is inserted into thechuck pieces, it is secured by the nut 414 at its rear section. Morespecifically, the chuck sleeves 412 are pushed backward along thetapered angle at α° by being tightened by the nut, and the spacesurrounded by them is restricted to hold the work (W).

[0130] A driven rotary section 415 is located opposite the drivingrotary section 407, and is rotatably mounted on the slidable framework416 so as to rotate vertically. The slidable framework 416 slides on theside frame 404 along the length of the apparatus. The slidable framework416 includes slide members 418 secured to side frames 417 between whicha front transverse frame 419 and a rear transverse frame 420 arearranged. More specifically, the slidable framework 416 has a slidingsurface in the outside of the side frame 417 and the bottom surface ofthe sliding member 418, and slides along the side frame 404 of the baseplate 403.

[0131] The driven rotary section 415 includes an outer sleeve 422 inwhich an inner sleeve 423 is rotatably carried, the outer sleeve 422having a pivot 421. The inner sleeve 423 is provided with a male threadin its rear section, and an inside space 423 a having a side tapered atβ°. The inside space 423 a houses chuck sleeves 424 and a sleeve 425.The chuck sleeves 424 are pushed forward by tightening the nut 426provided in a rear section, so that the chuck sleeves are split intoseveral chuck pieces among which the work (W) is held.

[0132] A hydraulic cylinder 427 as a pressing device 409 is providedbetween the mount 410 of the base plate 403 and the front transverseframe 419 of the slidable framework 416. No controller for regulatingthe hydraulic cylinder or no switch are illustrated. When the work (W)is to be compressed held by the driving rotary section 407 and thedriven rotary section 415, the hydraulic cylinder 427 is extended so asto shorten the distance between them. A repulsive force involved in thecompression is set off in the base frame, so that no load is applied tothe lathe (M). Instead of the single-acting cylinder, a double-actingcylinder can be employed, which enable the finished work (W) to bereadily taken out of the apparatus.

[0133] The driven rotary section 415 is provided with a biasing device428 for biasing the work (W). The biasing device 428 includes a bracket429 in which an inside space 429 a receives a rotating shaft 430 havinga female thread. The rotating shaft 430 has a threaded rod 432 providedwith a handle 431. The threaded rod 430 is rotated by the handle 431. Atthis stage, because of the abutment of the lower end of the threaded rod432 with the top surface of the rear transverse frame 420 the threadedrod 432 is prevented from upward and downward movement but the rotaryshaft 430 is caused to move up or down together with the outer sleeve422. In this way the driven rotary section 415 is vertically rotatedaround the pivot 421.

[0134] The apparatus 401 is operated as follows:

[0135] The inner sleeve 411 of the driving rotary section 407 isconnected to the chuck (T) of the lathe (M). At the same time, thetapered shaft 402 is connected to the tail stock of the lathe (M).

[0136] Subsequently, the driving rotary section 407 and the drivenrotary section 415 are aligned, thereby setting the biasing device 428free. The work (W) is inserted between the chuck sleeves 412 and 424spaced at a predetermined distance (D). The work (W) is firmly held bytightening the nuts 414 and 426.

[0137] The lathe (M) is driven to operate the hydraulic cylinder 427 soas to rotate the work (W) and compress it between the chuck sleeves 412and 424.

[0138] While the work (W) is subjected to rotation and compression, thehandle 431 is operated to rotate the driven rotary section 415. At thisstage, the distance (D) is shortened, and therefore, the diametralexpansion advances. The continued compression is effective to protectthe work (W) from breaking owning to bending back. When a desireddiametral expansion is finished, the rotary sections 407 and 415 arereturned to a position where they are aligned under the maintainedrotation and compression. When the work (W) is straightened up, therotation and compression are stopped, followed by the withdrawal of thework (W).

[0139] In this embodiment, the torque is given by a lathe which isprotected from an unfavorable repulsive force of the compression. Thisensures that all-purpose lathes can be employed.

[0140] In the embodiments referred to above the work (W) is a solidmetal shaft but it can be hollow like a pipe. Now, referring to FIGS. 37to 44, the diametral expansion of a metal pipe will be described:

[0141] In general, if a machine or a device must be partly be elastic orhermetic, expansion joints or bellows for flexible pipes are used. Aprocess for making bellows is known in the art; one example is describedin Japanese Patent Publication 3-42969 which teaches the method ofinjecting a bulged fluid pressure into a metal pipe. As the internalpressure is increased, the pipe is expanded in accordance with thecontour of the mold. However, a disadvantage is that the expanded wallbecomes thin. The present invention is directed to diametrically expandmetal pipes without reducing the thickness of the expanded portion.

[0142] A work (W) is held by a pair of rotary holders aligned at adistance (D). The rotary holders are similar in structure to a chuck ofa lathe. If the work (W) is short, a chuck sleeve which can compress oneend of the work (W) is used.

[0143] The distance (D) can be varied between a few tens of millimetersand a few hundreds of millimeters.

[0144] In this situation at least one of the rotary holders is rotatedto rotate the work (W). The rotating speed depends upon the material andthe size of the work, covering a few to a few hundreds of rotations perminute. If the speed is slow, the diametral expansion takes time, and ifit is too fast, it is difficult to follow pressure to a plasticdeformation, thereby resulting in the possibility of breakage due tofatigue.

[0145] Then the work (W) in rotation is subjected to compression, whichis applied in a known manner such as a hydraulic jack or a hydrauliccylinder. The strength of the compressive force depends upon thematerial, the diameter, and the thickness of the work (W). However, inthis embodiment the compressive force can be smaller than that requiredin the bulge process.

[0146] While the work (W) is subjected to rotation and compression, itis bent by biasing one of the holders with respect to the axis of theother holder. As a result, the work (W) is bent while being in rotation.The angle of bend is a few to a few tens of angle; if it is too small, adesired diametral expansion is not obtainable. If it is too large, thework (W) is likely to become damaged.

[0147] If the work (W) is bent while it is in rotation, a largecompressive force acts upon the inside of the bent portion, therebycausing plastic deformation to arise there. Because of the plasticdeformation, the work (W) deforms in a direction in which thecompressive force escapes; that is, the work (W) diametrically expands.Because of the rotation the plastic deformation spreads around theperiphery of the work (W). At this stage it is important to apply acompressive force to outside the bent portion. If a pull acts upon thisoutside of the work (W), the work (W) is alternately subjected toextension and contraction, and finally fractures owing to fatigue. Asthe work (W) diametrically expands, the distance (D) between the holdersbecomes short. Accordingly, the pressure is constantly applied to one ofthe holders to move toward the other holder, so as to continue to applythe compressive force to the periphery of the work (W). In this way,because the work (W) is subjected to compression and bending while it isin rotation, the compressive force can be smaller than that required inthe bulge process.

[0148] After the desired diametral expansion is finished, the work (W)is straightened up by returning the rotary holders until they arealigned again under the continued compression applied inside and outsidethe bent portion. If the compression is reduced, the work (W) is liableto fracture owing to expansion and contraction. After the straighteningis finished, the application of the compressive force is stopped,followed by the withdrawal of it.

[0149] Because of the rotation and bending applied to the work (W) whilebeing subjected to compression axially applied to the work (W), itbecomes shorter than before the diametral expansion is performed. Thismeans that the shortened portion is absorbed in the expanded part,thereby increasing the thickness of the expanded metal flesh. This isadvantageous over the bulge processed pipes.

[0150] Referring to FIGS. 37 to 44, the illustrated apparatus 501includes a pair of side walls 503 erected on base plates 502 on thefloor, and a rectangular framework 504 which is provided with a drivingrotary holder 505.

[0151] The driving rotary holder 505 includes an inner sleeve 507rotatable in an outer sleeve 506 secured to a member 505 a of theframework 504. The inner sleeve 507 is provided with a driven rotarygear 508 at its rear end, and houses chuck sleeve 509 for holding a work(W) in an inside space 509 a axially produced. The chuck sleeve 509 isprovided with a slit portion 509 b which is tightened by a bolt 511through a fastener 510. In this way the work (W) is firmly held in thechuck sleeve.

[0152] A motor 512 is provided under the rotary holder 506, having itsoutput shaft provided with a driving gear 513 engaged with the drivengear 508.

[0153] Opposite the driving rotary holder 505 is provided a drivenrotary holder 514 which includes a slider 516 slidable along rails 515on the framework 504. A ring-shaped rotary framework 517 is rotatablyconnected to the slider 516 by a pivot 518. The ring-shaped rotaryframework 517 is secured to an outer sleeve 519 in which an inner sleeve520 is rotatably housed. The inner sleeve 520 houses a chuck sleeve 521,which has the same structure as the chuck sleeve 509, includes an insidespace 521 a axially produced to receive the work (W). The work (W) inthe inside space 521 a is firmly held by narrowing a slit portion 521 bwhich is tightened by a fastener 522.

[0154] The slider 516 is provided with a feeder 523 designed to move thedriven rotary section 514 toward and away from the driving rotarysection 505. The slider 516 is provided with a bracket 524 in its rearend on which a bearing 525 is provided. The framework 504A is providedwith an opening 526 in its rear transverse frame 526, and a sleeve 527secured in its front end. The sleeve 527 is provided with a slit 527 athrough which a projection 528 a of a shifter block 528 is extruded. Theshifter block 528 is caused to move to and fro along the length of theapparatus 501.

[0155] A feeder rod 529 is rotatably carried by the bearing 525 and thetransverse frame 526. The feeder rod 529 is provided with a male threadportion on its periphery with which the shifter block 528 is engaged.The feeder rod 529 is provided with a stop ring 530 at its front end toprevent it from slipping off, and a handle 531 in its rear end.

[0156] Below the driven rotary section 514 is provided a pressing device514, which causes the driven rotary section 514 to move toward thedriving rotary section 505, in the form of a hydraulic jack 533 providedon the base plate 502. A cam 535 is rotatably supported on the hydraulicjack 533 such that it can vertically rotate by means of a pivot 534. Thecam 535 includes an engager 535 a engageable with the rear portion ofthe slider 516, and a receiver 536 to receive an upward urge of the jackby coming into abutment with a piston rod of the jack 533.

[0157] A biasing device 537 is provided on the driven rotary section 514so as to effect the up and down movement of it. The biasing device 537includes a nut 538 secured to the outer sleeve 519, and a threaded rod539 engaged with the nut 538. The threaded rod 539 is placed in abutmentwith the slider 516 it its lower end, and is provided with a handle 540in its upper end. The rotation of the handle 540 causes the threaded rod539 to rotate, but because of abutment of its lower end with the topsurface of the slider 516 the threaded rod 539 does not move up or down,and the nut 538 engaged with it moves up and down together with theouter sleeve 519. In this way the driven rotary section is caused torotate vertically.

[0158] In operation, the two rotary sections 505 and 514 are arrangedsuch that the respective holders 507 and 520 are aligned, which meansthat the biasing device is prevented from its biasing work. A work (W)is held between the chuck sleeves 509 and 521 wherein a target portionfor the desired diametral expansion is placed in agreement with the rearend of the chuck sleeve 509, and the a fixing member 510 is arranged ata position of the slit 509 b. Then the work (W) is firmly held bytightening the chuck sleeve 509 with the nut 511.

[0159] The chuck sleeves 509 and 521 are positioned at a predetermineddistance (D). This distance (D) is based on a calculation that a desireddiametral expansion is achieved. To adjust the distance (D), the handle531 is operated to cause the shifter block 528 to move backward untilits projection 528 a comes into abutment with the rear end of the slit527 a, and is further operated to cause the feeder rod 529 to advancegradually. As the top end of the feeder rod 529 is connected to theslider 516, the driven rotary section 514 is advanced along the rails515 until the desired distance (D) is reached, where the fastner 522 isfitted in the slit 521 b in the chuck sleeve of the driving rotarysection to hold the work (W).

[0160] Subsequently, the pressing device 532 is operated to axiallycompress the work (W), and the motor 512 is operated. The compression iseffected by operating the hydraulic jack 533 and rotating the cam 533 inthe direction indicated by the arrow (FIG. 39). The energization of themotor 512 causes the work (W) held by the chuck sleeves 509 and 521 torotate. In this way, the work (W) is subjected to compression while inrotation. The rotating speed can be a few to a few tens of rotations perminute. Then, the biasing device 537 is operated to bend the work (W) atan angle of 3° to 7°.

[0161] Experimentally, this embodiment was applied to a carbon steelpipe having an outside diameter of 22.2 mm, and a thickness of 1.6 mm soas to expand the diameter of a middle portion of it up to 27 mm coveringa width of 7 mm around the periphery. As a result, it has beenascertained from this experiment that the rotating speed is 4 rotationsper minute, the angle of bend is 6°, and the compression is 1 to 2 tons.

[0162] As is evident from the foregoing description, the work (W) isdiametrically expanded between the chuck sleeves 509 and 521 by beingsubjected to compression, rotation, and bending. As the processadvances, the original distance (D) is shortened but the compressioncontinues. If it is stopped, the work (W) is subjected to detrimentalrepetition of bending and straightening, and is liable to fracture.After the desired diametral expansion is finished, the biasing device isreturned to its original position so as to straighten up the bentportion in the work (W) under the constant compression. Then therotation and compression are stopped, and the finished work (W) is takenout of the apparatus.

[0163] Initially the work (W) is loosely held between the chuck sleeves509 and 521 but as the rotation, bending and compression advance, thediametrically expanded portion is tightly held by the chuck sleeves 509and 521, thereby making it difficult to take the work out of theapparatus. Therefore, the withdrawal of the work (W) is helped by thehydraulic jack 533 in a manner in which it is slid backward, and the cam535 is lowered in the opposite direction to the arrow direction (FIG.39). The fastener 522 is unfastened, and the driving rotary section 505is separated from the driven rotary section 514 to release the work (W).A pin 541 is drawn, and the frame 504 and the transverse frame 526 arereleased so as to allow the driven rotary section 514 to slide backwarduntil the work (W) is released. Finally, the fixing member 510 isunfastened, and the work (W) is withdrawn from the driving rotarysection 505.

ADVANTAGES OF THE PRESENT INVENTION

[0164] The present invention makes it easy to diametrically expand ametal shaft or pipe, whichever it is solid or hollow. Gears and cams canbe readily provided in a desired portion of metal shafts without weldingor mass-cutting. The production of mechanical power transmissions isfacilitated.

1. A method for diametrically expanding a metal shaft, comprising thesteps of: holding the shaft between a pair of holders spaced at adistance (D); rotating the work around its axis, moving one of theholders toward the other holder so as to compress the work; biasing oneof the holders in a direction which crosses the axis of the otherholder, so as to bend the work and build up bulged portions accruinginside the bent portion around the periphery of the work within thedistance (D) until a desired expansion is achieved; and straightening upthe work; wherein the compression is constantly applied to both theinner and outer sides of the work to be bent, and the rotation isinitiated at the latest immediately after the bending is started, andthe straightening-up is performed under the continued compression androtation.
 2. The method according to claim 1, wherein the compression isrelatively low at the initial stage of the diametral expansion, andprogressively increases as the diametral expansion advances.
 3. Anapparatus for diametrically expanding a metal shaft, comprising: adriving rotary section (4) and a driven rotary section (6) arranged at apredetermined distance, each of the rotary sections comprising holdersfor securing a work between them; a driver (5) for operating the drivingrotary section (4); a pressing device (8) for axially compressing thework held by the holders; and a biasing device (7) for declining theaxis of the work; wherein the pressing device (8) applies thecompression to one of the rotary sections (4) and (6), and the biasingdevice (7) declining the other rotary section (4) or (6).
 4. Anapparatus for diametrically expanding a a metal shaft, comprising: adriving rotary section (103) and a driven rotary section (105) arrangedat a predetermined distance, each of the rotary sections comprisingholders for securing a work therebetween; a driver (104) for operatingthe driving rotary section (103); a pressing device (109) for axiallycompressing the work held by the holders; and a biasing device (108) fordeclining the axis of the work; wherein either the driving rotarysection (103) or the driven rotary section (105) is arranged rotatablyaround a pivot (107 a) provided in a direction perpendicular to the axisof the work, and the rotatably arranged rotary section is supported bythe pivot (107 a) so as to enable the simultaneous inspection of theinner and outer sides of the bent portion of the work.
 5. The apparatusaccording to claim 4, further comprising a slidable frame (106) providedon the base plate (102), and a rotary framework (107) rotatablyconnected to the slidable frame (106) through a bearing, and wherein thedriving rotary section (103) is secured to the base plate (102) and thedriven rotary section (105) is secured to the rotary framework (107). 6.An apparatus for diametrically expanding a metal shaft, comprising: adriving rotary section (205) and a driven rotary section (225) arrangedopposite each other, each of the rotary sections comprising holders forsecuring a work between them; a driver (214) for rotating the work heldby the holders around its axis; a first slidable pressing device (206)for causing the driven rotary section (225) to move toward and away fromthe driving rotary section (203); a biasing device (230) for rotatingthe driven rotary section so as to decline with respect to the axis ofthe holder of the driving rotary section; a second slidable pressingdevice (226) for shifting the axis of a pivot rotated by the biasingdevice (23) toward and away from the driving rotary section; and adisplacing device for shifting the center of rotation between theholders in accordance with a sliding distance covered by each of thefirst pressing devices (206) and the second pressing device (226).
 7. Anapparatus for diametrically expanding a metal shaft, comprising: adriving rotary section (205) and a driven rotary section (225) arrangedopposite each other, each of the rotary sections comprising holders forsecuring a work therebetween; a driver (214) for rotating the work heldby the holders around its axis; a biasing device (230) for rotatingeither the driving rotary section (205) or the driven rotary section(225) with respect to the axis of the holder of the other rotarysection; a first slidable pressing device (206) and a second slidablepressing device (226) for moving the driving rotary sections (205) and(225) toward and away from the axis of a pivot (223) rotated by thebiasing device (23); and a displacing device for shifting the axis ofthe pivot between the holders in accordance with a sliding distancecovered by each of the two pressing devices (206) and (226).
 8. Anapparatus for diametrically expanding a metal shaft, comprising: a pairof rotary sections (325) and (326); a holder provided in each of therotary sections for holding a work; a sliding device (311) for causingat least one of the rotary sections to move toward and away from theother rotary section; a biasing device (319) for declining at least oneof the rotary sections with respect to the axis of the other rotarysection; a driver (332) for rotating the work held by the holders aroundits axis; and a transmission (336) for transmitting the torque of onerotary section to another so as to effect the synchronous rotation ofthe two rotary sections (325) and (326).
 9. The apparatus according toclaim 8, wherein the transmission (336) comprises a rotating division inwhich rotatable brackets (338) are provided, having a pair of splines(339) interposed between them, the splines comprising gears (340)engaged with follower gear (333) provided in the rotating division,thereby transmitting a torque of one of the rotating division to theother.
 10. An apparatus for diametrically expanding a metal shaft,comprising: a driving rotary section (407) provided with a first workholder and being capable of rotating the work held by the holder; adriven rotary section (415) provided with a second work holder on anopposite side to the holder of the driving rotary section (407) andbeing capable of moving toward and away from the driving rotary section(407); a biasing device (428) for declining the second holder withrespect to the axis of the first holder; and a pressing device (409) forpressing the driven rotary section (415) toward the driving rotarysection (407); wherein the driving rotary section is driven by anarrangement in which the first work holder is connected to a chuck of alathe (M) so as to utilize the torque of the lathe (M).
 11. Theapparatus according to claim 10, wherein the pressing device (409) isplaced between a base plate (403) and a slidable frame (416), andwherein the base plate (403) is provided with a tapered shaft (402), thetapered shaft and the first work holder being connected to the lathe(M), thereby compensating a repulsive force involved in operating thepressing device within the base plate.